油气润滑ECT传感器的管道电容及其影响

采用COMSOL软件建立油气润滑电容层析成像传感器的三维物理模型,推导计入管道电容的数学模型;定义管道电容影响系数,分析管道厚度和管道半径对其影响.在算法中计入管道电容对环状流进行图像重建,并对重建图像质量进行评价.研究结果表明:管道电容影响系数可以表征管道电容对测量电容的影响;管道厚度增加或管道半径减少,管道电容对测...     

油气润滑测试系统的ECT传感器优化设计

建立油气润滑测试系统中的电容层析成像技术(ECT)传感器模型,运用COMSOL软件,以环状流为典型流型,获取电容值和灵敏度场信息。以重建图形质量综合评分(OS)最优为目标,Design-Expert软件为平台,对电容传感器结构参数进行正交实验设计与优化。结果表明,单因素对OS值影响的由强到弱的顺序为绝缘管壁厚度归一值、极板张角、屏蔽层与绝缘管道的间距归一值;采用优化后结构参数的传感器,重建图像质量得到了较大的提高,表明Design-Expert软件可高效、准确地对ECT传感器结构参数进行设计和参数优化,为同类研究提供了参考。     

油气润滑ECT传感器的建模与边缘电容分析

基于小管径油气润滑ECT系统中电容传感器的特点,建立其电容传感器的二维数学模型;分析相对介电常数对边缘电容的影响;定义边缘电容影响系数,并研究边缘电容影响系数与管道半径的关系。研究结果表明:管壁、油膜与气体的厚度比对边缘电容值有显著的影响,通过减小油膜厚度及管壁厚可以有效减小边缘电容;小管径的边缘电容影响系数超过0.5,随着管径增大,边缘电容影响系数呈下降趋势;对于油气润滑系统来说,传感器的边缘电容对ECT空间图形成像误差有较大影响。     

基于最大类间方差法的油气润滑测试系统ECT图形重建

提出一种基于最大类间方差法的油气润滑测试系统ECT图形重建的改进算法。该算法在Landweber迭代算法的基础上,将油气润滑管道内的气相分布作为背景,液相分布作为目标,使用最大类间方差法获得油气两相错分率最小的灰度阈值,并在此基础上建立基于图像灰度的油膜厚度测量方法。仿真结果表明,与线性反投影算法(LBP)和Landweber算法相比,基于最大类间方差法的图形重建算法可有效消除成像中的伪影现象,得到清晰的油气界面,计算可获得准确度较高的油膜厚度。此外,该算法还具有程序简单,成像精度高的特点。     

油气润滑测试系统中ECT软场效应研究

电容层析成像系统的传感器具有\"软场\"特性,即敏感场分布受被测介质的影响。为获得高质量的重建图像,利用COMSOL软件快速求解油气润滑测试系统ECT的灵敏度矩阵,运用COMSOL和MATLAB联合仿真,对该管道内层流和环状流2种典型流型的灵敏度场的软场效应进行分析,并且应用LBP算法和OTSU算法,分别在考虑和忽略软场效应的情况下对2种流型进行图像重建。仿真结果表明,软场效应改变了灵敏度分布;润滑油介质靠近管壁时,检测敏感度较高;采用软场效应改变的灵敏度矩阵进行图像重建,将有效提高重建图像精度。     

油气润滑ECT系统图像重建中病态问题分析

建立油气润滑ECT系统图像重建的数学模型,分析油气润滑ECT系统图像重建中产生病态性的主要原因和影响因素。采用条件指标-方差分解比(CIVDP)方法,对油气润滑ECT系统图像重建中灵敏度矩阵的病态进行诊断分析。分析表明:油气润滑ECT系统图像敏感场的灵敏度矩阵列向量间存在很强的复共线性关系,即存在很强甚至严重的病态性;油膜厚度和极板数目影响图像重建的病态性,通过对灵敏度数据列的回归分析与残差处理,可有效削弱病态程度。     

油气润滑ECT系统传感器设计

运用SolidWorks软件和COMSOL软件建立三维ECT管道模型,通过分析与比较传感器在空/满场状态下的电容值得到了三个结构参数(电极的张角、极板的长度、管道与屏蔽层的间隔)的优化范围,并定义了传感器电容响应率指标、对传感器性能进行了定量分析。在此基础上,基于正交实验的方法,以传感器性能综合评价函数OPT为目标,运用COMSOL软件和Design-Expert软件对上述三个结构参数进行了优化。研究结果表明:①当传感器结构参数为最佳参数组合时,函数OPT值为7.2087,与实际仿真获得的OPT值之间的相对误差为3.36%;②设计的传感器具有较均匀的灵敏度分布和较高的成像质量。     

油气润滑系统的ECT系统的设计

论文根据油气润滑系统小管径管道检测的特点,提出了一种带有电容补偿的电容层析成像系统,分析了该电路工作原理,并对系统中的关键组成模块的电路进行了仿真,给出了补偿电容的测量时的算法流程,最后基于三个重要的系统评价指标对设计的ECT系统进行评价,结果表明:该ECT系统具有检测时间短、抗杂质性电容能力强、稳定性和动态响应性能好等特点。     

油气润滑ECT系统的RBF图像重建算法研究

采用COMSOL软件建立了油气润滑环状流管道与ECT系统的三维物理及有限元模型,结合电磁场理论获取了传感器的电容值;建立了电容值与成像灰度值一一对应的的RBF映射模型;提出了RBF算法并应用于油气润滑两相流动的图像重建过程;以图像相对误差(IME)和图像相关系数(CORR)为评价指标对该算法的进行实验验证.研究结果表明...     

提高ECT系统成像质量和速度的方法

在电容层析成像(ECT)技术的应用中,图像重建的质量和速度是电容传感器,并通过一种改进的正则化算法和利用DSP系统来实现快速高质的图像重建.     

A novel method of plotting sensor sensitivity field and image reconstruction algorithm for electrical capacitance tomography system

Sensor sensitivity field in electrical capacitance tomography is affected by the distribution of multiphase medium, which is the peculiarity of soft field. This brings great difficulty for image reconstruction. To improve the quality of image reconstruction, it is important to analyze the distribution of the sensitivity field. In this article, using the finite element method, we expound a kind of novel plotting pattern to field, which is the distribution of sensitivity field through computer simulation. From experiments and results of sensitivity field analysis, a novel method of image reconstruction based on genetic algorithms is presented. The finite element model is correct and simulation result is fine by adopting unequal interval plotting patterns. At the same time, the result of image reconstruction has high precision. __________ Translated from Chinese Journal of Scientific Instrument, 2005, 26(3) (in Chinese)     

基于MCMC方法的电容成像图像重构算法

研究基于概率统计的电容成像图像重构算法,以马尔科夫随机场的方式给出介电常数分布的先验概率,利用电容成像(electrical capacitance tomography,ECT)线性模型得到似然函数,通过马尔科夫链蒙特卡罗(Markov chain Monte Carlo,MCMC)方法对介电常数分布的后验概率密度进行采样,马尔科夫链的转移核利用Metropolis-Hastings方法得到,结合嵌套迭代提高计算效率。仿真结果表明,嵌套迭代-MCMC方法在正则化参数设置合适的条件下,可以得到较好的图像质量,基于MCMC方法图像重构算法为解决ECT图像重构问题提供一种新思路。     

非闭合电极电容层析成像传感器在冻土测试中的应用

为了实现电容层析成像技术对冻土冻结冰峰面的在线、非侵入测试,研制出了满足冻土测试要求的非闭合电极电容层析成像传感器,并对该种传感器的电容分布特性进行了实测;确定出了适合冻土测试的的高、低介电常数的标定物质;搭建了冻土一维冻结实验系统.对含水量8%的湿土样冻结过程的冰峰面迁移进行了电容层析成像测试,并利用IMNSNOF图像重建算法重建出了冻结过程各时刻的冻结截面物质分布图像,由图像可确定出冻土中已冻土、未冻区以及冰峰面的位置.电容层析成像测试结果与温度测试结果相吻合.     

循环流化床上ECT传感器灵敏场的有限元分析

电容层析成像传感器的敏感场受多相流介质分布的影响,软场特性给图像重建带来很大困难,为了提高重建图像质量,对敏感场分布进行分析是非常必要的.该文以12电极方形电容传感器为基础,对电容层析成像技术应用于循环流化床研究做了简单阐述,着重研究了用有限元法对方形电容传感器敏感场分布的计算机仿真,讨论了负敏感场的处理方法.     

OPTIMAL DESIGN AND FABRICATION STEPS OF ELECTRICAL CAPACITANCE TOMOGRAPHY SENSORS

Electrical capacitance tomography (ECT) is a non destructive technique for obtaining the distribution of some physical quantity in a closed pipe by measuring the permittivity distribution. Several conducting plates are fixed around the circumference of the pipe so they do not disturb the flow or movement of materials. The imaging quality of an electrical capacitance tomography system depends upon many co-influential parameters such as number of electrodes, length and width of electrodes, axial guard electrodes, radial guard electrodes, and screen guard. Optimum selection of these variables coupled with advancements in sensing electronics and imaging algorithm provides the best inside view of a closed vessel/pipe. This, in turn, provides better process information for control. This article is intended to summarize such design rules for ECT electrodes and sensors. Numerical simulations were performed using commercially available finite element method (FEM) software to help verify the optimality of the design parameters chosen. Experimental verification was conducted using a fabricated capacitance sensing circuit that could measure capacitance in the range of 1 fF to 7999 femtofarads with a root means square noise level of 0.07 fF. Some parameters such as the thickness of the pipe are chosen as demanded by the process. This article will be useful for researchers to design the ECT Sensors with ease.     

Data fusion in dual-mode tomography for imaging oil–gas two-phase flow

Process tomography (PT) techniques have been developed rapidly for visualizing the internal behavior of industrial processes, e.g. multi-phase flow measurement. Most of tomography systems employ a single measurement technique, such as computerized tomography (CT), optical tomography (OT), electrical resistance tomography (ERT) or electrical capacitance tomography (ECT). It is now possible to fit two or more tomographic systems to an industrial process. Detailed information from different modalities can be gained by inspection of separate tomographs, and the advantage of the strongest features provided by each unit can be taken. A combined tomogram can be produced of superior quality to any of the separate tomograms. To maximize the information available from the combined tomographic system, data fusion is the better option. In this paper, a dual-mode tomography system based on capacitance sensor and gamma sensor was developed to capture oil–gas two-phase flow. The two modalities can work at the same time. Two fusion methods, namely image fusion method and data fusion method, are proposed. Both simulation and static experiments for oil–gas two-phase flow were conducted. The reconstruction results of different fusion methods and modalities were compared and discussed.